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Tooth Regeneration: Grow Your Teeth Like an Alligator!
#1
This is post no. 1 under the main topic.
Although the mere notion of the alligator teeth could give us creeps, scientists hope that within these scary jaws lies the clue for successful tooth regeneration in humans. A latest research appeared in the journal Proceedings of the National Academy of Sciences, in May 2013, provides an insight into the regulation of multiple tooth regeneration of the American alligator. The researchers predict that understanding the mechanisms related to the development and renewal of tooth in this crocodile model will be useful in finding a way to stimulate the teeth regrowth in adult humans.

Alligator teeth are not that different from ours!

Crocodiles exhibit the same complex dental architecture and morphological characteristics as mammals such as thecodont teeth (teeth that are embedded in sockets). They also have a secondary palate like that of the mammals. In addition, unlike humans, they have the capability of renewing their teeth many times within their lifetime. Thus the alligators can be considered a classic model to be used in tooth regeneration studies.

One crocodile tooth renews about 50 times

Crocodiles are polyphyodont i.e., their teeth are continuously shed and replaced during the existence of the animal. It is estimated that one crocodile may replace each of its 80 tooth about 50 times throughout its lifespan. Humans however, are diphyodont, meaning that they can grow only two successive sets of teeth within their lifetime: the deciduous (milk) teeth, which are followed by the permanent (adult) teeth. After that they lose their ability for tooth renewal.

The present study observed that each tooth of an alligator behaves like a complex ‘family unit’. Each of these units comprises of a functional tooth which is the most mature tooth, a successional tooth that will later be developed in to a functional tooth and the dental lamina. These components were found to be at different stages of development. Furthermore, the researchers were able to identify a type of cells in the dental lamina of the alligators which they suspect to be dormant teeth stem cells that can be activated when a functional tooth is shed or extracted.

The research also provides information about the signalling molecules that plays a critical role in tooth development and renewal of the alligators.

Humans may have the potential for tooth regeneration

Dental lamina, the source of odontogenic stem cells for cyclic tooth regeneration, usually begins to degrade in humans after the generation of secondary tooth. Thus the humans lose the ability of regenerating their adult teeth. However, a remnant of it still exists and may initiate odontogenic tumors later in life. Previous literature reveals the presence of teeth stem cells in adult humans. Although these cells retain the ability of differentiation, they cannot generate a whole new tooth.

the following video can provide a basic idea of human tooth development.




No more dentures!

Tooth loss is a common problem that may occur due to various reasons including fractures, physical injuries, tooth decay and infections of the gum. Though this condition is rarely critical, it often results in aesthetic and psychological concerns thus necessitating in replacement of tooth.

Current options available for tooth replacement include techniques such as dental implants made out of biocompatible materials like titanium that can be inserted in the teeth bone. However the success of these implants is not completely satisfactory in terms of their performance and long-term stability. Therefore, many recent researchers focus on the potential of odontogenic stem cells to grow living tooth with proper functional characteristics. Several studies report regeneration of teeth using stem cells in vitro, although their use in dental practice is still challenging owing to factors such as high risk of rejection.

The current research however, promises of a future potential of regeneration of teeth in vivo. These findings suggest the possibility of using this knowledge for stimulating the dormant stem cells present in the remnant human dental lamina to initiate tooth regeneration process. In addition, the researchers hope that this will help in treating oral diseased that involve supernumery teeth formation.

Reference

Wu, P., Wu, X., Jiang, T. X., Elsey, R. M., Temple, B. L., Divers, S. J., ... & Chuong, C. M. (2013). Specialized stem cell niche enables repetitive renewal of alligator teeth. Proceedings of the National Academy of Sciences.

http://www.pnas.org/content/early/2013/0...0.abstract
 
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#2
This is post no. 2 under the main topic.
This is a very interesting approach to teeth regeneration, especially because it is intended to be performed in vivo.

Dr. Duanqing Pei and his team from the Chinese Academy of Sciences and Guangdong Provincial Key Laboratory of Stem Cell Biology and Regenerative Medicine have described a method of using stem cells in order to regenerate human teeth. The stem cells they used in this process were isolated from urine, which is a very preferable option for many reasons. First, obtaining stem cells from urine is very easy and non-invasive, and second, those are somatic stem cells which are known to be much less susceptible to tumor formation than embryonic stem cells. The tooth would be grown from stem cells of the same person, so there would be no rejection related problems.

This team succeeded to transform urine stem cells into pluripotent stem cells in their lab, and then the cells were implanted into mice. After three weeks, there were new structures noticeable that looked like teeth. They had dentin, pulp, and enamel. It was a good start, but the teeth were not as hard as normal teeth and they missed nerves and blood vessels. Obviously, more research in this field has to be done.

There are some controversial opinions about using urine stem cells for this purpose. Prof Chris Mason from University College London suggested that urine stem cells can be the source of contamination and that their efficacy is not strong enough. He also pointed out that these cells are not so common in urine, so that makes them less favorable option.
However, stem cells have promising future in teeth replacement. There are many new approaches on the horizon such as 3D printing. Scientists are hoping to use 3D printed teeth with stem cells as a base for stem cells growth. That way, the stem cells could eventually replace the artificial material, building a proper replacement for human teeth.
Sasa Milosevic
 
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#3
This is post no. 3 under the main topic.
Urinary stem cells

The previous article in this thread refers to a study that suggests urinary stem cells (USCs) as potentially useful in tooth regeneration but also points out reservations that some scientists have about USCs. Notwithstanding these concerns, various research groups, most notably in China, have been exploring the potential of these cells in other contexts. For example, one study used USCs in a study on genitourinary reconstruction in mice. They infected genitourinary reconstruction with adenovirus expressing mouse vascular endothelial growth factor (VEGF) and mixed the infected USCs with human umbilical vein endothelial cells (HUVEC) in a collagen gel before implanting the gels into athymic mice. They found that the mixture of cells resulted in grafts that were well-vascularised and contained more cells containing endothelial and smooth muscle markers and nerve fibres than in grafts using uninfected USCs. In another study, the viability of USCs after storage in urine for 24 h was assessed. Approximately 100 USC clones derived from stored urine were found to maintain features including expression of mesenchymal stem cell surface markers, high telomerase activity, and bipotent differentiation capacity. Furthermore, they could be induced to express urothelial cell-specific markers and barrier function upon exposure to urothelial differentiation medium. Thus despite reservations in some quarters, the potential of USCs is being explored and may prove to be of value in stem cell therapeutic approaches in a variety of contexts.

Sources

LANG, R. et al., 2013. Self-renewal and differentiation capacity of urine-derived stem cells after urine preservation for 24 hours. Plos One, 8(1), pp. e53980-e53980

WU, S. et al., 2011. Implantation of autologous urine derived stem cells expressing vascular endothelial growth factor for potential use in genitourinary reconstruction. The Journal of urology, 186(2), pp. 640-647
 
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#4
This is post no. 4 under the main topic.
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